Berge, Z. (1997).  Computer conferencing and the online classroom.
International Journal of Educational Telecommunications, 3 (1), 3-21.
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This is a good synthesis paper that captures both the pros and the cons of
computer conferencing, synchronous and asynchronous.  There are three
categories of CMC: computer conferencing (e-mail, group conferencing
systems, and interactive messaging systems), informatics (making documents
accessible via CMC), and computer-aided instruction (particularly suitable
for distance learning environments).  

Advantages: time independence of asynchronous conferencing is convenient
for student work, self-paced learning allows time to compose responses,
whereas synchronous conferencing allows CSCW and real-time discussion and
brainstorming.  Computer conferencing fosters engaged learning that uses
peer review/support activities and projects, allows mentoring and
apprnetice models to be used, and fosters the role of the student as a
lifelong learner, a self-directed, responsible learner.  It provides a
"paper trail" of archived messages and documents, and access to all the
world's people and resources.

Disadvantages: low social context cues may promote a more egalitarian
classroom atmosphere, but do not support body language and other nonverbal
cues that help students avoid misunderstandings in communication.  It
often fosters less inhibited behavior - can even lead to flaming.
Textbased interface favors learners who are good at expressing their
thoughts in written form.  Information overload can overwhelm new users,
especially before they have developed their own filtering and
classification schemes.  There is also an urgent need for expert technica
support and maintenance of hardware, software, and networks, and practice
time for new users until the technology becomes transparent enough to them
so they can focus on the course content rather than the use of the
delivery system.  "Computer anxiety" plagues some new users who feel they
are talking into an unresponsive vacuum or missing face-to-face
interaction.

With regard to putting thoughts into writing, here are a few excerpts:

pro:  "before participants respond to postings, they can take time to
reflect and consider their response, and they can accumulate data and
references with which to substantiate their arguments and positions.  This
permissible time lag in computer conferencing is particularly well suited
to shy, thoughtful, or hesitant conversationalists and to members of those
cultures where answers and responses are considered and carefully framed
before presentation" (p. 8).  [I can relate to that!!]

pro/con:  "...currently the advantages of this text-based communication
include a perception by some learners that written communication is more
reflective than spoken interaction.  The very act of assembling one's
thoughts and articulating them in writing for a conference audience
appears to involve deeper cognitive processing.  Additionally, students
have commented that the practice in writing helps them improve their
English and writing skills" (p. 10).  [Is the converse true - those with
poor writing skills will tend to avoid CMC for that very reason? Need to
investigate that.]

"Finally, the text-based nature of computer conferencing favors those
users who are both articulate and good with the language of the written
discussion" (p. 13).

He also mentions other factors such as the lack of visual/social cues that
are present in face-to-face interaction, the increased work necessary to
keep up with the topics so they can actively participate in a thoughtful
way, etc.

Besides going in detail through the various advantages/disadvantages of
CMC vs. the traditional classroom environment, he mentions that the type
of instruction designed by professors that utilizes computer conferencing
mirrors their assumptions (implicit theories) about what constitutes a
"good education".  Hence, those with constructivist leanings will tend to
emphasize a learner-centered approach and collaborative learning - the
characteristics of the teaching/learning experience that Jones et al. call
"engaged learning" - and which tend to increase independence,
self-direction, and self-reliance among students.